1. Field of the Invention
The present invention relates generally to a stator of an electric rotating machine and a method of manufacturing the stator, and more particularly to the stator wherein a stator winding formed of a series of conductive segments is wound on a stator core.
2. Description of Related Art
An electric rotating machine such as an alternator has a stator and a rotor to generate an alternating current in the stator from a rotating force added to the rotor or to generate a rotating force in the rotor from an alternating current applied to the stator. The stator has a cylindrical stator core and a stator winding wound on the core, and the alternating current is received or generated in the winding. The rotor is rotatably disposed in a central hole of the core.
The core has a plurality of slots aligned along a circumferential direction thereof, and each slot penetrates through the core along an axial direction of the core. The winding is formed of a plurality of conductive segments inserted into the slots, and the segments are serially connected with one another to form a coil end group on an axial end side of the core. The winding is wound on the core so as to heighten a conductor occupying ratio and to compactly form the coil end groups. The ratio is defined as a ratio of an area actually occupied by the segments to a total area allowed for the winding.
Each segment is, for example, formed in a U shape so as to have two straight portions and a U-shaped head portion. To manufacture a stator having the winding wound on the core, the head portions of the segments are twisted so as to widen a span between the straight portions of each segment, the straight portions of each segment are, respectively, inserted into two slots so as to penetrate through the slots, and end portions of the segments protruded from the slots are bent and inclined toward the circumferential direction of the core to form oblique portions as a coil end group on an axial end of the core. In another technique, end portions of the segments not yet inserted into the slots are bent and deformed into oblique portions, and the straight portions of each segment are, respectively, placed into two slots such that the oblique portions are protruded from the slots as a coil end group on one axial end of the core. In these circumstances, each slot receives four straight portions of four segments aligned along a radial direction of the core to form four layers of the oblique portions along the radial direction. Ends of the oblique portions of each pair of segments inserted into different slots and disposed adjacent to each other along the radial direction are closely aligned with each other along the radial direction so as to form an end pair. Then, each end pair is connected with each other by welding to serially connect the segments with one another. Therefore, the winding composed of a series of segments is wound on the core to form a stator.
Published Japanese Patent First Publication No. 2001-197709 discloses a method of twisting a plurality of U-shaped conductive segments to produce a stator winding from the twisted segments. In this method, to obtain a stator winding of a stator used for an alternator of a vehicle, four segments are inserted into each slot of a stator core, portions of the segments protruded from the slots are twisted by using a twisting device to form oblique portions bent by the device and standing portions held by the device.
This method is described with reference to FIG. 1, FIG. 2 and FIG. 3 in more detail. FIG. 1 shows a segment set 103 to be inserted into slots 102 of a stator core 101, and FIG. 2 shows one segment set deformed by a twisting device. FIG. 3 is a perspective side view of a coil end group formed of all segment sets twisted.
As shown in FIG. 1 and FIG. 2, a stator winding is formed of a plurality of segment sets 103. Each segment set has a U-shaped larger segment 131 and a U-shaped smaller segment 132. The segment 131 is shaped so as to have a U-shaped head portion 131a, first oblique portions 131b and 131c and two straight portions. The segment 132 is shaped with the segment 131 so as to have a U-shaped head portion 132a, first oblique portions 132b and 132c and two straight portions. The four straight portions of one segment set are inserted into each pair of slots 102 away from each other by one magnetic pole pitch to place both an inserted portion 131d of the segment 131 and an inserted portion 132d of the segment 132 in one slot and to place both an inserted portion 131e of the segment 131 and an inserted portion 132e of the segment 132 in the other slot. Further, two straight portions of another segment set are inserted into each slot. Therefore, four segments form four layers aligned along a radial direction of the core 101 in each slot. Each layer extends along the circumferential direction. Then, a twisting device (not shown) holds ends of all segments 131 and 132 protruded from the slots 102 and twists the segments 131 and 132 so as to form second oblique portions 131f and 131g bent by the device, standing portions 131h and 131i held by the device, second oblique portions 132f and 132g bent by the device and standing portions 132h and 132i held by the device.
The second oblique portions 131f and 131g are inclined toward a circumferential direction by half of one magnetic pole pitch to extend away from each other, and the second oblique portions 132f and 132g are inclined toward the circumferential direction by half of one magnetic pole pitch to approach each other. Each of the standing portions 131h, 131i, 132h and 132i extends along an axial direction of the core 101 so as to stand on an axial end of the core 101. The portions 131f to 131i of the segments 131 and the portions 132f to 132i of the segments 132 form a coil end group on one axial end of the core 101.
Each of the standing portions 131h, 131i, 132h and 132i acts as a margin so as to be held by the twisting device and extends along the axial direction of the core 101 so as to stand on the core 101. As shown in FIG. 3, the standing portions 131h, 132h, 132i and 131i of the segments 131 and 132 forming an inner layer, a first middle layer, a second middle layer and an outer layer in that order are aligned along the radial direction.
Then, the standing portions 131i and 132i of each pair of segments 131 and 132 adjacent to each other along the radial direction are connected with each other by welding to form a first row extending along the circumferential direction, and the standing portions 131h and 132h of each pair of segments 131 and 132 adjacent to each other along the radial direction are connected with each other by welding to form a second row extending along the circumferential direction. Therefore, the segments 131 and 132 are serially connected with one another so as to form four layers and two rows.
In the twisting, the segments of each layer are bent and moved along the circumferential and axial directions, independently from the segments of the other layers. Accordingly, not only the segments protruded from the core 101 can be positioned in the circumferential direction for each layer, but also the segments can easily be positioned in the axial direction for each layer, independently from the positioning in the circumferential direction.
For example, in the twisting, the movement of the segments of the outer layer is larger than the movement of the segments of the inner layer. However, even when the height of portions of the segments protruded in the axial direction from the core in each layer is set before the twisting process to be the same as that in the other layers, the axial height of the segments in each layer can easily be set after the twisting process to become equal to that in the other layers. Further, the segments protruded from the core can easily be deformed for each layer in the twisting process so as to have a desired shape matching with various requirements. That is, because the standing portions in all layers have the same axial height, the standing portions adjacent to each other along the radial direction can easily be connected with each other.
Further, Published Japanese Patent First Publication No. 2000-350421 discloses a connecting method wherein end portions of conductive segments adjacent to each other along a radial direction of a stator core are connected with each other by welding to form a winding of a stator used for an alternator of a vehicle. FIG. 4 is a view of a segment connecting device in this Publication, and FIG. 5 is a view showing the connection of two end portions aligned in a pair.
As shown in FIG. 4 and FIG. 5, a stator core 114 wound by a series of U-shaped conductive segments is disposed on a board 106. Both end portions 121 of each conductive segment are deformed in the same manner as the standing portions shown in FIG. 2, so that each end portion 121 extends in the upper direction. Insulating films of the end portions 121 are removed in advance by using a cutter, chemicals or the like. Four end portions 121 are aligned along a radial direction of the core 114 to form four layers, and a plurality of end portions 121 are disposed at equal intervals along a circumferential direction of the core 114 for each layer. Two end portions 121 of the inner and first middle layers adjacent to each other along the radial direction are in contact with each other to form an end pair 113, and the end pairs 113 of the inner and first middle layers form an inner row. The two end portions of the outer and second middle layers adjacent to each other along the radial direction are in contact with each other to form another end pair 113. The end pairs 113 of the outer and second middle layers form an outer row. The two end pairs 113 aligned along the radial direction are disposed at a sufficient interval, so that the end pairs 113 can be electrically insulated from each other.
In an electrode restraining process, the end portions 121 are restricted on the core 114 by a restricting device 107 to place each end pair 113 at a predetermined position. The device 107 has an inner side electrode 110, an outer side electrode 111 and a comb-shaped electrode having a plurality of bar-shaped electrodes 112. The electrode 110 is disposed to be in contact with inner side surfaces of the end portions 121 placed in the inner layer. The electrode 111 is disposed to be in contact with outer side surfaces of the end portions 121 placed in the outer layer. The electrodes 110 and 111 restrain the end portions 121 in the radial direction. Each electrode 112 is disposed between two groups of four end portions 121 facing each other in the circumferential direction so as to be in contact with side surfaces of the eight end portions 121. The electrodes 112 restrain the end portions 121 in the circumferential direction to act as protective elements. Further, the electrodes 112 bridge a gap between the electrodes 110 and 111. A width of each electrode 112 in the circumferential direction is widened toward the outer side of the core 114, so that the electrode 112 is reliably in contact with the end portions 121.
In a directly-earthed arc welding process, a welding torch 109 of a segment connecting device 110 is moved by a robot arm 108 to be placed over a particular end pair 113 which is positioned at a welding starting position in the outer row. Then, a welding voltage is applied between the torch 109 and the restricting device 107, and an inert gas is supplied to the torch 109. Further, after the welding voltage is applied, the board 106 is rotated clockwise while a distance between the torch 2 and the device 107 is maintained. During the rotation of the board 106, the welding voltage is fixed, and the position of the torch 109 is fixed. Therefore, end portions 121 of the particular end pair 113 placed just under the torch 109 are first welded together, and end portions 121 of another end pair 113 adjacent to the welded end pair 113 are welded together. That is, the end portions 121 of the end pairs 113 in the outer row are successively welded together.
After the welding for all end pairs 113 in the outer row is completed, the torch 109 is moved to be placed over another particular end pair 113 which is positioned at a welding starting position in the inner row. Then, the end portions 121 of the end pairs 113 in the inner row are successively welded together. After one rotation of the board 106, the rotation of the board 106 is stopped, and the supply of the welding voltage and the inert gas is stopped. Further, the electrodes 110, 111 and 112 are removed. Therefore, a stator winding having a plurality of segments serially connected with one another is obtained so as to form four layers and two rows.
Assuming that the twisting method disclosed in the Publication No. 2001-197709 is combined with the connecting method disclosed in the Publication No. 2000-350421, conductive segments inserted into a stator core are twisted according to the twisting method such that segments protruded from the core in the layers have substantially the same axial height, and the twisted segments are serially connected with one another to form a stator winding. In this case, because a distance between the torch 109 and end portions 112 of the end pairs 113 becomes constant during the rotation of the core in the welding process, the connecting device 110 can weld the end portions 112 of each end pair 113 together without excessively increasing heat added to the end portions 112. Therefore, in the welding process, the heat is hardly transmitted to the second oblique portions of the segments covered with insulation films. Accordingly, heat deterioration of the insulation films covering the second oblique port ions can be suppressed. Further, because the heat deterioration of the insulation films is effectively suppressed, an area of a film removal portion in each segment can be reduced. In this case, electrical insulation between end pairs 113 adjacent to each other in the radial direction can reliably be achieved, and a distance between the end pairs 113 aligned along the radial direction can be shortened. That is, a coil end group of the segments can be compactly formed in the radial direction.
Further, in the electrode restricting process, each group of four end portions 112 aligned along the radial direction can be restrained in the radial direction and circumferential directions by the electrodes 110, 111 and 112, and the end portions 113 of each end pair 113 can be earthed through the electrodes 110, 111 and 112 so as to be smoothly welded together.
Moreover, the electrodes 112 cover the second oblique portions of the segments from the torch 109 so as to shield the second oblique portions from arc discharges of the torch 109. Therefore, the electrodes 112 prevent heat of the arc discharges from being transmitted to insulation films of the second oblique portions. Further, the electrodes 112 are in contact with large side surfaces of the end portions of the segments, so that a heat dissipation area between each electrode 112 and the end portions of the segments becomes large. Accordingly, heat of the arc discharges outputted from the torch 109 can be effectively dissipated to the electrodes 112, this effective dissipation suppresses the excessive heating of the second oblique portions, and insulation films of the second oblique portions are hardly damaged by the heat of the arc discharges.
Problems in the prior art disclosed in the Publication No. 2001-197709 and the Publication No. 2000-350421 are described hereinafter.
The prior art discloses the method of producing a winding of a stator used for an alternator of a vehicle, and a series of conductive segments wound on a stator core is formed in four layers and two rows to act as a stator winding. In contrast, a traction motor for a vehicle representing an electric rotating machine has been required in recent years. This motor is required to output a larger amount of electric current set at a higher voltage, as compared with the current and voltage in the alternator. Therefore, in this traction motor, conductive segments are wound on a stator core in many layers (e.g., eight layers) and many rows (e.g., four rows) to increase the number of turns in a stator winding. In this case, to manufacture the motor in a small size, it is required to further lessen an axial height of a coil end group (i.e., portions of segments protruded from a stator core) and to compactly form the coil end group.
However, assuming that stator winding based on the prior art is used for a traction motor, it is difficult to manufacture the motor in a small size. For example, in the prior art disclosed in the Publication No. 2001-197709, it is necessary for the standing portions 31h, 31i, 32h and 32i of the segments to be held and twisted by the twisting device, and the standing portions are disposed so as to stand on a stator core toward the axial direction. Therefore, a length of a stator along the axial direction is unnecessarily increased by an axial height of the standing portions, so that the motor becomes large in size.
Further, in the prior art disclosed in the Publication No. 2000-350421, as shown in FIG. 5, because the electrodes 112 are in contact with the film removal portions 121 corresponding to the standing portions, a length of each film removal portion 121 is required to be larger than a thickness of the electrode 112. Therefore, the film removal portion 121 is undesirably lengthened.
Moreover, it is desired that the conductive segments are disposed at smaller intervals to form a stator in a smaller size. However, in this case, there is a probability that the insulation performance of the conductive segments will be degraded. Assuming that an axial length of the standing portions is increased to heighten the insulation performance, an axial height of a coil end group is further increased, so that a stator further becomes large in the axial direction.
In recent years, a small-sized electric rotating machine efficiently generating electric power or rotational force has been required. That is, in a small-sized alternator or electric motor efficiently operated or generating a high voltage, it is desired that conductors disposed in slots of a stator core and conductors protruded from the slots as coil ends are disposed as densely as possible. Therefore, each of the conductive segments is formed of a straight angle wire formed in a rectangular shape in section, wires are disposed at smaller intervals, and the number of turns in a stator winding is increased. In this case, the segment is thinned, the number of end portions of segments to be connected with one another is increased, and a gap between end pairs is shortened. As a result, it is required to produce a stator winding with high precision. Further, it is desired to maintain a high degree of freedom in design even when the intervals of the segments are shortened, to maintain the insulation performance and reliability of the winding, and to stably and preferably weld end portions together at high speed.
In conclusion, in the manufacturing of a stator composed of a stator core and a series of conductive segments wound on the core in many layers and rows, it is important to provide a stator winding having small-sized coil ends in the axial direction of the core and a method of manufacturing the stator without increasing the number of parts or the number of assembling processes while the insulation performance and reliability are maintained in the winding.